Optical Transport Test Solution

1. Overview

The development of optical network transport technology went through various stages, such as PDH, SDH, SONET, MSTP, OTN,DWDM and PTN tester.

In actual optical network, the transport technologies contain PDH, SDH, SONET, MSTP, OTN, DWDM and PTN under construction.

OPWILL could offer different test technologies according to different optical transport technologies, for example PDH/SDH/SONET(from 1.5M to 10G/40G) test, MSTP(GFP/VACT/LCAS) test, OTN (OTU1/OTU2/OTU3) testand update the latest transport technologies supporting PTN (MPLS-TP/OAM) network test.

2. PDH/SDH/SONET network test

SONET/SDH networks have stood the test of time and, until recently, they have been primarily used to transport aggregated voice signals and private-line frame-relay and ATM services.The growth of these high-revenue-generating services over the years has resulted in large-scale deployments of metropolitan and long-haul SONET/SDH networks worldwide. SONET/SDH networks development lead to the exact test requirement of SONET/SDH technologies.

The traditional SONET/SDH test mainly focus on specifications of SDH transport system. The test range can generally be several types:

ü         Transmission capability test, including BERT test, mapping and demapping test to describe SDH transmission payload capability;

ü         Pointer test ,including timing excursion, payload output jitter test and etc. to reveal SDH asynchronous work capability;

ü         Overhead test, including alarm and performance monitoring function test, protocol analysis and etc. to make sure the overhead function;

ü         Protect switching test, including various protect switching conditions and time test to guarantee quick task recovery once in trouble.


1) BERT Test

In SDH transmitting side, it constitutes normal STM-N frame structure with PRBS encapsulated as payload into special VC and overhead then to send them to NUT through SDH. 

In receiving side, SDH demapping VC and recover BERT test of PRBS to make sure whether VC integrated or not.

Finger 1  SDH BERT Test

2) Mapping Test

According to the setting of under test network path and mapping relation, SDH tester will select corresponding path and configuration to offer branch input single constituted with special PRBS mapping into NUT then send to NUT;  in receiving side, SDH recovers test brand single through mapping handling. To check the brand single integrality through BERT test could also test the mapping process.

Finger 2 SDH Mapping Test

3) Pointer Test

         Transmitter: the transmitter and the receiver of SDH work asynchronously. The transmitter generates test VC with PRBS and penetrates the VC into SDH single path whose timing benchmark is not synchronous with NUT; through transmitting adjusted VC pointer value to make VC and NUT synchronous.    

         Receiver: In NUT output, test VC to SDH signal frame will appear motion. Because SDH tester receiver is asynchronous with NUT, it will recover test VC through proper pointer handling. And to check out VC integrality through BERT test.

         Through SDH tester receiver, users can calculate pointer adjusting values in certain time to test and measure NUT frequency deviation between timing benchmark and test origin on. 

Finger 3  SDH Pointer Test

4)Alarm Test

Test whether the response and disposal of NUT to alarm signal accord with the standards.

SDH tester sends an alarm signal embedded in POH or SOH to NUT.

Receiver: including upstream and downstream signal , check the alarm response signal from NUT. Such as LOS, LOF and LOP, some AIS. AIS are different because of different affected maintenance levels. Besides, the other alarm signals will be set up. Once checked AIS, LOS, LOF in multiplex section, the MSOH up will send out FERF.  

Finger 4  SDH Alarm Test


5) PM Test

         Through SDH tester insert Bit Error to B1, B2, B3 bytes to generate B1, B2, B3 Error and then send to NUT.

         At receiver, check the response of NUT through SDH tester. When BIP codes in high-order or low-order path error, NUT will generate FEBE indication connecting with up-link SDH tester to check out FEBE calculation right or not.

Finger 5  SDH PM Test

6) Protocol Test

It generates various overhead signals through SDH tester, such as alarm condition or BIP error, or special spending contents.

The NMS of NUT will respond to the standard or not.

Finger 6  SDH Protocol Test

3 MSTP Network Test

         MSTP/MSPP have allowed SONET/SDH to evolve with the times and offer an efficient means of transporting packet-based services over the widely deployed SONET/SDH networks. Traditional SDH is used for load TDM service while MSTP achieves Ethernet and Optical transmission and multi tasks insertion and loading in SDH network through GFP, VCAT, LCAS. MSTP uses GFP as encapsulation technology and adopts VCAT and LCAS to adapt different bandwidth and adjusts link capability in certain range. 

Finger 7  MSTP Network


MSTP network test does not only contain traditional SDH/PDH test, Ethernet test but also the maintenance and test of new technologies which include the consistency of GFP. VCAT and LCAS and features test and interworking test among equipment suppliers.

1 GFP Consistency Test

ü         Validate whether NUT or equipment obey GFP ITU-T G.7041

ü         GFP mapping and demapping

ü         GFP overhead control

ü         GFP Error/Alarm insertion and analysis

Finger 8  GFP Test


2 VCAT Consistency Test

ü         Validate whether NUT and equipment obey ITU-T G.707

ü         Support HO and LO VCAT container

ü         VCAT Error and Alarm Insertion: Single/Multi member insertion

ü         Latency test, each member inserts differential delay and analysis

Finger 9  VCAT Test

3 LCAS Consistency Test

ü         Validate whether NUT or equipment obey ITU-T G.7042

ü         Source or destination simulation, create LCAS messages manually/automatically

ü         Analysis and test LCAS messages/status and alarm

ü         Validate LCAS function ( increase or delete member, failure recovery and etc.)

Finger 10  LCAS Test


4 MSTP install and Troubleshooting

After MSTP network construction, it is necessary to test and check the network to achieve network designed index and SLA through end-to-end Ethernet test.

Finger 11  MSTP On-line Testing

         In daily MSTP network maintenance, the network faults involve not only in SDH level but also GFP, VCAT, LCAS and Ethernet service and data link level. Users need to check out and locate the troubles and eliminate on time.  

Finger 12  MSTP Maintenance Testing


SDH test module of OPWILL could offer an ideal EOS diagnostic scheme. The test module can be used in all the relative layers after configuration and insertion to any monitoring point in straight-through mode.

OTM2500 test module supports wide next-generation SDH testing, including deep GFP frame analysis and GFP, VCAT, LCAS error and alarm monitoring. The final layer fault diagnosis is Ethernet layer in the condition of no fault source. The field engineer could put the Ethernet data into OTM2600 test module through OTM2500 Ethernet  interface and doing Ethernet frame and alarm/error analysis comprehensively.


4 OTN Network Test

OTN (Optical Transport Network) is a new type of optical transport system based on ITU-T G.709, G.870, G.872, G.798 and so on. OTN combines the advantages traditional SDH/SONET and WDM well and supplies monitoring system and network survivability system in each layer.

In optical field, OTN could handle large grained to supply transparent transport capability of lager grained 2.5G, 10G, 40G with WDM system high speed and high capacity features.  

In electrical layerOTN could apply the operational and managed capability of SDH/SONET to WDM system through asynchronous mapping and multiplex to form a high capacity transmission network featured with large grained broadband transmission service feature.

OTN network test mainly focus on OTN technology specifications which can be divided into several types as followings:

ü         Mapping test

ü         Alarm/Bit Error generate and monitor

ü         Overhead generation and capture

ü         Protect service disruption test

ü         Through mode test


1)Mapping Test

OTN tester could do ODU multiplex and de-multiplex of OTN signal. OTU could encapsulate various signals to mapping BULK, SDH (STM-16/64), Ethernet and etc. OTN tester will send OTU encapsulation signals to OTN equipment/network to validate whether OTN network can meet ITU-T G.709 standard or not.

Finger 13 OTN Mapping Test

2) Alarm/Error Generation and monitoring

OTN tester sends alarm/error of OTU, ODU, OPU layer to OTN equipment/ network to validate whether OTN equipment/network responds correctly or not. OTN analyzer could also analysis and disposal the alarm/error from OTN equipment/network correctly.  

Finger 14 OTN Alarm and Error Test

3) Overhead Generation and Capture

OTN tester could edit, analysis and disposal OTN signal overhead.

Finger 15 OTN Overhead Test

4) Protect Service Disruption Time Test

         OTN tester could connect with OTN equipment/network to test and record OTN service disruption time. The trigger condition could select the alarm generated at service disruption to test the quick recovery capability at fault point.  

Finger 16 OTN SDT Testing

5 Through Mode Test

OTN signals in network could punch through OTN tester transparently after connecting OTN tester with OTN network. OTN tester could analysis the alarm, error, overhead and so on information of OTN signal and meanwhile insert alarm/error, rewrite overhead to simulate trouble situation in real network and test OTN network operation capability.



Finger 17 OTN Through Mode Test

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